1. Field of the Invention
The present invention relates to isolated polypeptides having tyrosinase activity and isolated polynucleotides encoding the polypeptides. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides.
2. Description of the Related Art
Enzymatic protein modification is frequently used, e.g. in food processing. One purpose of such protein modification is improvement of texture of the food material. Texture is not only related to sensory perception, but also to stability, water holding capacity, gelling and emulsifying properties. Enzyme-aided structure engineering, e.g. via protein cross-linking, can therefore be exploited in several food applications, such as in meat, fish, dairy and cereal foods.
Enzymes having tyrosinase activity have previously been shown to be able to cross-link food proteins. Cross-linking may take place via the formation of o-quinones from protein-bound tyrosine. These o-quinones either condense with each other or react with free amino and sulfhydryl groups present in proteins.
Enzymes for industrial applications are preferably extracellular. Extracellular enzymes, such as secreted enzymes, are usually more stable and can more readily be produced in industrial scale by recombinant technology.
Enzymes having tyrosinase activity have previously been reported. See e.g. WO2006084953 disclosing extracellular tyrosinases obtainable from Trichoderma spp. and suggesting various uses of such tyrosinases. At least one of the Trichoderma spp. tyrosinases disclosed is proteolytically processed at its C-terminus, whereby about ⅓ of the protein is cleaved off. According to literature, fungal tyrosinases are activated in vivo by limited proteolytic cleavage (Decker, H. and Tuczek, F. (2000) Trends Biochem. Sci. 25, 392-397).
It is an object of the present invention to provide polypeptides having tyrosinase activity and polynucleotides encoding the polypeptides. Another object of the present invention is to provide polypeptides having tyrosinase activity which can be industrially produced in high amounts in a stable form. Another object of the present invention is to provide polypeptides having tyrosinase activity which have a higher specific activity as compared to known tyrosinases. Such polypeptides are useful in production of various food products, e.g. due to their ability to cross-link food proteins. Yet another object of the present invention is to provide methods for producing polypeptides having tyrosinase activity.